Cohen, who was long known as Trump's fixer, said in open court that he made illegal campaign contributions "in coordination and at the direction of a candidate for federal office."
Here are some of the key reactions to the news.
Lanny Davis, attorney for Michael Cohen:
"Michael Cohen took this step today so that his family can move on to the next chapter," Davis said in a statement. "This is Michael fulfilling his promise made on July 2nd to put his family and country first and tell the truth about Donald Trump. Today he stood up and testified under oath that Donald Trump directed him to commit a crime by making payments to two women for the principal purpose of influencing an election. If those payments were a crime for Michael Cohen, then why wouldn't they be a crime for Donald Trump?"
Rudy Giuliani, counsel to President Donald Trump:
"There is no allegation of any wrongdoing against the President in the government's charges against Mr. Cohen. It is clear that, as the prosecutor noted, Mr. Cohen's actions reflect a pattern of lies and dishonesty over a significant period of time," Giuliani said in a statement.
Michael Avenatti, the lawyer representing Stormy Daniels, in an interview on MSNBC after news of the guilty plea:
"Count eight relates to my client, Stormy Daniels, and let me just say this. She has been vindicated this afternoon. I have been vindicated based on what we've gone through over the last five to six months, what she's gone through and I applaud her courageousness and fortitude in coming forward. I think a lot of this stems from her courage and what she was willing to come forward and do," Avenatti said in the MSNBC interview.
"The $130,000 payment -- count eight -- absolutely directly relates to her, that was a payment that was made to her. It relates to the president of the United States, Donald Trump. And we're going to get to the bottom now in connection to the civil case as to what the president knew and when he knew it and what he did about it. I mean the likelihood... of me getting a deposition of the President of the United States under oath just went through the roof. No question about it and that our case is no longer going to be stayed and we're going to press forward as aggressively as possible," he said.
Democratic National Committee chair Tom Perez:
"No one was closer to Donald Trump than Michael Cohen. As his longtime lawyer and 'fixer,' Cohen was at the center of Trump’s inner circle, and today he admitted to breaking the law at Trump’s direction in order to influence the 2016 presidential election. The seriousness of this development cannot be overstated. The culture of corruption that Donald Trump brings with him everywhere is a disgrace to the presidency and a threat to our democracy," Perez said in a statement put out by the DNC.
Preet Bharara, former U.S. Attorney for the Southern District of New York:
"Michael Cohen in a courtroom in SDNY, under oath, declared that the President directed him to commit a federal crime," Bharara wrote on Twitter.
"I am seldom stunned. But I am."